1. Field of the Invention
The invention relates to an electronic circuit with a trimming capacitor consisting of a flexible metal lug as a first electrode and a rigid counter electrode, the metal lug being arranged in confronting relationship with the counter electrode.
2. Description of the Prior Art
Trimmers are variable capacitors usually of small capacitance values. They serve for trimming and possibly readjusting critical circuits, usually oscillatory circuits. After the trimming operation their capacitance should no longer vary, for example, by mechanical influence or vibrations.
For input stages of radio and television apparatus, so-called tuners, a trimmer is known in which a sheet metal lug inside the sheet metal housing of the tuner is bent with respect to the wall of the housing to vary the capacitance.
When the sheet metal lug is bent in the direction of the wall of the tuner housing acting as mass, the capacitance is increased and when it is bent away from the wall of the housing the capacitance is reduced.
In this construction it has proved disadvantageous that the wall of the housing of the tuner is used as an electric counter electrode; pressure exerted on the housing of the tuner, for example, only by manipulation, can bend the wall of the housing, be it slightly, and hence the capacitance of the trimming capacitor is varied. For this reason an improved trimming capacitor has been suggested (German Patent Application No. P 31 10 084.8) which consists of a flexible metal lug arranged before a metal surface, the metal surface consisting of a U-shaped profiled sheet metal rigidly connected to an insulating carrier, the metal lug being provided oppositely to a major surface of the profiled sheet metal. Although with this embodiment the disadvantage has been removed that the capacitance is varied involuntarily, so for example by manipulation of the circuit in which the trimming capacitor is incorporated, the necessity exists to provide a U-shaped profiled sheet metal as a counter electrode opposite to the flexible metal lug, which required an additional process step.
It is the object of the invention to improve the electronic circuit with trimming capacitor described in the opening paragraph in such manner that the additional process step of incorporating a U-shaped profiled sheet metal as a counter electrode can be dispensed with but that the known advantages are maintained, namely that an unwanted movement of the capacitor electrodes by mechanical load and hence an undesired capacitance variation is avoided.